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We demonstrate a new method to reverse the polarity and charge transport behavior of naphthalenediimide (NDI)-based copolymers by inserting a vinylene linker between the donor and acceptor units. The vinylene linkers minimize the intrinsic steric congestion between the NDI and thiophene moieties to prompt backbone planarity. The polymers with vinylene linkers exhibit electron n-channel transport characteristics under vacuum, similar to the benchmark polymer, P(NDI2OD-T2). To our surprise, when the polymers are measured in air, the dominant carrier type switches from n- to p-type and yield hole mobilities up to 0.45 cm² V-1 s-1 with hole to electron mobility ratio of three (μh/μe, ∼3), which indicates that the hole density in the active layer can be significantly increased by exposure to air. This increase is consistent with the intrinsic more delocalized nature of the highest occupied molecular orbital of the charged vinylene polymer, as estimated by density functional theory (DFT) calculations, which facilitates hole transport within the polymer chains. This is the first demonstration of an efficient NDI-based hole semiconducting polymer, which will enable new developments in all-polymer solar cells, complementary circuits, and dopable polymers for use in thermoelectrics. [ABSTRACT FROM AUTHOR]

We present here the synthesis, characterization, and transistor performance of three semiconductor materials based on trans-1,2-(dithieno[2,3-b:3′,2′-d]thiophene)ethene derivatives. Although the incorporation of aromatic, alkyl substituents in both ends of trans-1,2-(dithieno[2,3-b:3′,2′-d]thiophene)ethene have a negligible effect on the conjugation length and the energy gap, the subtle chemical modification leads to great variations in film microstructures, electronic properties, and packing arrangements. The appropriate substituents are capable of providing efficient molecular packing arrangements for high carrier mobility. The phenyl-substituted derivative, compound 3, demonstrates a remarkably high thin film FET performance, with mobility up to 2.0 cm2V−1s−1and on/off ratio up to 108. In addition, the devices show good environmental stability, even after storage in air for 7 months. [ABSTRACT FROM AUTHOR]

A novel method is described for the preparation of nearly monodispersed and highly magnetic responsive microspheres with magnetite nanocrystals formed in a polymeric matrix by hydrothermal reduction. The method is based on the formation of iron hydroxide/polymer composite microspheres by acid-catalyzed condensation polymerization of urea and formaldehyde in the presence of colloidal iron hydroxide. The iron hydroxide colloids entrapped in the polymer matrix are then in situ converted to magnetite nanocrystals by reaction with sodium borohydride under hydrothermal conditions. Characterization of the resulting microspheres with electron microscopy and vibrating sample magnetometry confirmed that these particles possessed a uniform spherical morphology, narrow particle size distribution, and high magnetic susceptibility. More interestingly, the magnetic nanoparticles embedded in the polymer matrix are of cubic shape and highly crystalline structure. While the growth of uniform composite microspheres is accounted for by the well-known LaMer model, the formation of the cubic magnetite nanocrystals appears to involve a dissolution−recrystallization process. After being coated with silica by the sol−gel approach, the magnetic particles were used as adsorbents for isolation of genomic DNA from biological samples, with results comparable to those obtained by magnetic silica microspheres. Incorporation of iron hydroxide colloids into polymer microspheres coupled with chemically induced phase transformation represents a new cost-effective approach to the preparation of uniform magnetic microspheres that is more controllable with respect to particle properties and more amenable to large-scale production. [ABSTRACT FROM AUTHOR]

Fluorinated single-walled carbon nanotubes (F-SWNTs) have been characterized by magic angle spinning 13C NMR spectroscopy and the results correlated with Raman, IR, and X-ray photoelectron spectroscopy measurements. The 13C NMR shift for the sp3fluorine-substituted (CF) carbon atoms of the SWNT sidewall is observed at 83.5 ppm. This apparently unusual shift compared to those of most other tertiary alkyl fluorides is confirmed to be due to the CF moieties from ab initio calculations on an 80-carbon fragment of the 5,5 (armchair) SWNT and is in good agreement with the predominance of 1,2-addition rather than 1,4-addition of fluorine. The lack of observable scalar 13C−19F coupling for the CF carbon signal over a wide range of spinning speeds and at two different field strengths apparently results from interaction between 19F−19F and 13C−19F dipolar couplings and from magnetization exchange between the 13C doublet components caused by fluorine spin diffusion. The assignment of the 83.5 ppm peak is further confirmed by the correlation of its diminished intensity upon thermolysis of the F-SWNT (400, 450, and 550 °C) with the relative intensity of the D (disorder) band in Raman and the C:F ratio from X-ray photoelectron spectroscopy (XPS). On the basis of the XPS signal, it appears that the CF2defect units decompose at a lower temperature than the CF sidewall moieties, suggesting that cutting chemistry precedes sidewall functional group removal. We propose that, where a comparison of samples with a high degree of functionalization is required, NMR provides a much better quantification than Raman. However, where a comparison between samples with low levels of functionalization or large differences in degree of functionalization is required, Raman provides a much better quantification than NMR. [ABSTRACT FROM AUTHOR]

We demonstrate, for the first time, that organic−inorganic hybrid hollow nanospheres with controllable size (12−20 nm) and shell thickness (4−7 nm) can be successfully synthesized through the condensation of 1,2-bis(trimethoxysilyl)ethane (BTME) around an inorganic-electrolyte-stabilized F127 micelle under a mild buffer condition (NaH 2PO 4−Na 2HPO 4, pH ∼7.0). The hollow spheres feature microwindows with pore size about 0.5−1.2 nm on the shell, which allow the guest molecules to diffuse into the hollow cavities. It was found that the concentration of the buffer solution in the synthesis was crucial to the formation of hollow nanosphere. At a low buffer concentration (20−100 mM), the surfactant exists as individual micelle. A core/shell nanocomposite was formed by the deposition of BTME at the corona of individual micelle, which leads to the formation of organic−inorganic hybrid nanoparticles with hollow interior after the extraction of the surfactant. The aggregation of individual micelles was observed at higher buffer concentration (>200 mM), which favors the formation of irregularly shaped particles with ordered mesostructure. This work presents a novel and facile strategy to fabricate hollow nanospheres with microwindows, which provides a versatile platform for practical applications of organic−inorganic hybrid materials in a broad range of fields such as catalysis, encapsulation, and drug delivery, etc. [ABSTRACT FROM AUTHOR]

[100]Pnma is believed to be a tough diffusion direction for Li+ in LiFePO4, leading to the belief that the rate performance of [100]-oriented LiFePO4 is poor. Recent work revealed that reducing the dimension of the LiFePO4 phase to 12 nm in the [100] direction increased the extent of Li solid solution between LiFePO4 and FePO4, which produced an increase in the active population and excellent rate performance, but the lithiation/delithiation mechanism for this interesting phenomenon remains to be unraveled. Here we report, by using operando X-ray diffraction, the phase transition path involved in the lithiation/delithiation process is single-phase featured. This work presents one of the first experimental demonstrations that decreasing the dimension of LiFePO4 in the [100] direction to the LiFePO4/FePO4 equilibrium phase boundary width can improve the solid solubility of both the end solid solutions (LiαFePO4 and Li1-βFePO4) and decrease the miscibility gap of LiFePO4, demonstrating a highly orientation-dependent lithium miscibility gap. [ABSTRACT FROM AUTHOR]